Quantitative analysis of liquid samples using electrical conductivity measurements is known in the art. Previously, two-cell conductivity detectors were often used. In such apparatus, the conductivity measurement is based on the difference in conductivity between the two cells as the sample passes through one of the cells. The two cells are subjected to the same conditions, except for the presence of sample in the one cell, whereby the difference in electrical conductivity between the cells is directly attributed to the subject sample.
The Carlson U.S. Pat. No. 4,209,299 discloses the use of a single cell apparatus. When a single cell conductivity detector is used, a much greater reliance is placed on the stability of the baseline. Any changes in the conditions, such as temperature fluctuations or foreign substances, creates noises or drifts in the baseline. Additionally, when a single cell conductivity detector is used, such as disclosed by Carlson, high quality water is required since the presence of extraneous electrolytes interferes with signals from the conductive substance sought to be determined. An additional sample purification step is often required. When the detection of very low concentrations of a conductive volatile substance is desired, the purity requirement is heightened and the purification step becomes quite burdensome.
Additionally, conventional systems generally cannot tolerate samples with even moderate amounts of another dissolved substance such as salt, acid or sugar therein. These extraneous substances not only create noises in the baseline but also overwhelm the signal from the sample electrolytes.
Accordingly, a need exists for improved methods and apparatus for quantitative analysis of samples using electrical conductivity measuring techniques.